More than 600 Conservative councillors have signed up to campaign for a Brexit ahead of the forthcoming EU referendum, according to Leave.EU. The group exclusively revealed the figures to IBTimes UK after David Cameron announced Tory ministers would have a free vote on the historic ballot, which will be held before the end of 2017.

"We are the fastest growing grassroots movement in the country and the establishment have had to sit up and take notice," a Leave.EU spokesman told IBTimes UK. "We have signed up 200 UKIP councillors, as well as 25 Liberal Democrats, 130 Labour, over 600 Conservatives [and] lots of independents.

"We have a team of over 60 people working up and down the country bringing people from all walks of life together in order to educate people why they should vote to leave the EU."

The campaign, co-founded by Ukip donor Arron Banks, is competing with Vote Leave to be assigned the official Brexit campaign nomination from the Electoral Commission. The group has crucially secured the support of Eurosceptic firebrand Nigel Farage.

But the Ukip leader has seen the party's only MP Douglas Carswell and its other well-known figures, such as Suzanne Evans and Patrick O'Flynn, join the Vote Leave campaign.

Vote Leave has also recently appointed Robin Hunter-Clarke, who unsuccessfully competed for the Boston and Skegness seat at the general election, as the group's national co-ordinator for Ukip councillors.

However, the move may be premature as a Ukip spokesman explained to IBTimes UK that the party's national executive committee (NEC) has yet to decide which Brexit group Ukip will support. The body could also rule that Ukip members, including MEPs and councillors, would have to back whichever campaign the NEC chooses.

The latest opinion poll from YouGov for The Times, of more than 1,500 people between 17 and 18 December, put "leave" one point ahead of "remain" (42% versus 41% respectively).

UPDATE: 7 January

Vote Leave has revealed to IBTimes UK that they have signed up 205 Ukip councillors. But the campaign has not disclosed the number of councillors from other parties.

How many councillors have Leave.EU claimed to sign up?

Ukip: 200

Liberal Democrats: 25

Labour: 130

Conservatives: 600+